Dawn Spirals Down Closer to Vesta’s South Pole Impact Basin

byKen KremeronJuly 23, 2011

South Polar Region of Vesta - Enhanced View
NASA's Dawn spacecraft is spiraling down closer to Vesta. It obtained this highest to date resolution image centered on the south pole of Vesta with its framing camera on July 18, 2011 as it passed the terminator. The image has been enhanced to bring out more surface details. It was taken from a distance of about 6,500 miles (10,500 kilometers) away from the protoplanet Vesta. The smallest detail visible is about 1.2 miles (2.0 km). Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA. Enhanced and annotated by Ken Kremer

NASA’s Dawn Asteroid Orbiter is now spiraling down ever closer to the protoplanet Vesta - since arriving on July 16 – and capturing magnificent new high resolution images of the huge impact basin at the South Pole that dominates the surface. See enhanced image here.

The Dawn team just released a new image taken by the framing camera on July 18 as the orbiter flew from the day side to the night side at an altitude of 10,500 kilometers above Vesta, the second most massive body in the main Asteroid Belt between Mars and Jupiter.

NASA's Dawn spacecraft obtained this image centered on the south pole with its framing camera on July 18, 2011. It was taken from a distance of about 6,500 miles (10,500 kilometers) away from the protoplanet Vesta. The smallest detail visible is about 1.2 miles (2.0 km). Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

“Dawn acquired this image after it had flown past the terminator and its orbit began taking it over the night side of Vesta.”

“After having this view, the spacecraft resumed gradually spiraling around its new home, heading for survey orbit where it will begin intensive observations of Vesta,” Rayman told me.

Dawn will reach the initial science survey orbit in early August, approximately 1700 miles above the battered surface. Vesta turns on its axis once very five hours and 20 minutes.

Vesta suffered an enormous cosmic collision eons ago that apparently created a gigantic impact basin in the southern hemisphere and blasted enormous quantities of soil, rocks and dust into space. Some 5% of all meteorites found on Earth originate from Vesta.

“The south pole region was declared to be a large impact basin after the Hubble Space Telescope (HST) data and images were obtained,” elaborated Prof. Chris Russell, Dawn Principal Investigator from UCLA.

“Now that we have higher resolution images we see that this region is unlike any other large impact on a small body but much of our experience here is on icy bodies of similar size,” Russell told me.

Dawn’s new images of Vesta taken at close range from just a few thousand miles away, now vastly exceed those taken by Hubble as it circled in Earth orbit hundreds of millions of miles away and may cause the science team to reevaluate some long held theories.

“The team is looking forward to obtaining higher resolution data over this region to look for confirmatory evidence for the impact hypothesis. They are not yet willing to vote for or against the HST interpretation. Needless to say the team got very excited by this image,” said Russell.

Dawn will orbit Vesta for one year before heading to its final destination, the Dwarf Planet Ceres.

As I understand it is Vesta situated so it would have been an object of intense bombardment as Jupiter cleared its orbit. Collisions between Jupiter orbit sharing objects would have “hail stormed” Vesta.

In some estimate I read ~ 30 % of Vesta thickness could have been stripped even before that putative large impactor. So we could have it easier than we believed to see the mantle parts of a planetoid.

Its very exciting to see through the mantle layers and potentially even the solidified core (if thats what we are looking at). Its a unique opportunity to study planetary formation.

It makes sense to assume Vesta was pummeled by Jupiter’s influence however
according to wikipedia, the crater is 1 billion years or younger, and the late heavy bombardment is 4.1 to 3.8 billion years ago. If accurate; the southern impact is more recent then Jupiter’s influence. How big would the impactor have been to cause such damage i wonder?

Its early days to speculate, I look forward to more data and good science resulting from. It will be especially interesting to see the Gamma Ray and Neutron Detector data. If its an impact site then we should see some mineral evidence of the impactor. Go Dawn. !

Thank you, those ages would suit earlier stripping indeed! Since my memory is not explicit, I have to note that I can’t remember either the figure or what it was out of clearly. And no I can’t find the text again! :-/

But the impression remaining was that it was another process that could help see deeper compared to the pristine Vesta.

I don’t think the impactor have been said to be very large in mass. For the general crater of a hyper-speed impactor, the impactor radius is ~ 1/20th of the crater radius.

For impactors that are so large that their curvature is closer to the impacted body curvature (rather, their size compares to the curvature) that changes. Vesta looks more of the former than the latter to me.

True, but as I’ve already stated, comments are generally informal; it’s how people speak to each other everyday. For instance, the contraction “ain’t” is often heard in educated as well as uneducated speech, but you would not use it in formal writing.

I’m beginning to think Vesta and the rest of the asteroids in the belt was once a planet that suffered a cataclysmic event. Vesta does not look like it was formed by a collection of space dust & debris on its own. There also looks like there were “rips and tears” on its surface.

The total mass of the asteroid belt is estimated to be 3.0×1021 to 3.6×1021 kilograms, which is just 4% of the mass of the Moon. The four largest objects, Ceres, 4 Vesta, 2 Pallas and 10 Hygiea, account for half of the belt’s total mass, with almost one-third accounted for by Ceres alone.

The big question is if it is a planetoid or not. (Which build Earth, Venus and perhaps Mercury by impacting together.)

A planetoid would be large enough to sort out thermally, chemically and gravitationally to hydrostatic equilibrium, and hide all of its past as a collection of impact dust. Ceres and Mars* are believed to be separate planetoids, the former icy so cheating somewhat on the mass requirement.

Now Vesta isn’t spherical enough so it can’t manage it today. But perhaps it did a good enough job before the cooling and impact to make us expect it would look like what we see today.

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* That is new, but apparently it fits the simulations of planet formation with Jupiter starting to migrate inwards, keeping the asteroids and Mars from growing further by scattering the other planetoids, before migrating outwards to its present orbit.

Can you all see the gigantic spaceship that has landed in a crater at the peek of that gigantic mound? (O_o) Seriously, I’m wondering what image artifact I am looking at.

Speaking of that mound, I hear it is ~ 36 km high, supplanting ~ 21 km Olympus Mons as the highest peak in the solar system. With a little bit of luck we are indeed staring down on the innards of a planetoid around that.

36km high above what though? This is a question that has bugged me for a long time: how do planetary scientists determine “sea level” on a rocky object? There must be some qualifying properties before such a determination can even be made… if the object is too mishapen (like maybe the moons of Mars) it wouldn’t make much sense to measure any ‘mountains’.